The resistance of suprarenalectomlzed animals to a number of nonspecific poisons is markedly reduced, as has been shown by several independent workers (1-6). These observers employing such poisons as cobra venom, curare, morphine, diphtheria toxin and typhoid vaccine were able to demonstrate a striking difference in resistance between normal and suprarenalectomized rats. In comparing the results obtained in different laboratories with the same poison, considerable differences in the lethal dose appeared to exist. With some of the poisons, as for example, typhoid vaccine, it seemed likely that the difference could be explained by a lack of uniformity of the preparation. Inasmuch as this test may have considerable value in future experimental work, it seemed advisable to secure additional data concerning certain of these poisons in order to find a stable substance having a relatively constant ratio between the lethal dose for suprarenalectomized rats and that for normal rats. This ratio should be at least 1:20. If such a substance could be found, the test might be standardized. In our attempts to standardize this test, we have used, up to the present time, typhoid vaccine, chloral hydrate, sodium cyanide and histamine, and the results obtained may be summarized as follows:Typhoid Vaccine.--Marine and his coworkers (4) have shown that 75 per cent of rats are killed by 0.25 cc. of a standard typhoid vaccine within 8 days after suprarenalectomy. In a recent paper we showed (6) that suprareualectomized rats surviving in good condition are killed by typhoid vaccine in doses of 0.4-1 cc. at the height of susceptibility (5-7 days). On repeating these experiments, it was noted 5o3 on

There are many mooted problems connected with the thymus gland in spite of the numerous studies dealing with the embryology, comparative anatomy, histology, and pathology of this organ. KSlliker (1) in 1879 drew attention to the fact that the thymus has an epithelial anlage from the branchial clefts, and since that time many attempts have been made to explain how from this epithelial germ had arisen the finished structure of the organ, with its important elements--the retieulum, Hassall's corpusdes, and free lymphoid-like ceils. The lack of knowledge and the disagreement as to the origin and biological significance of the small thymic cell have been one of the main stumbling blocks towards a proper understanding of the functions of this organ. These cells have been the subject of contention among those who have worked in the field. Two schools have developed, each of which has during the last 25 years vigorously upheld its views. The Maximow-Hammar (2, 3)" group supported by Rudberg (4),Jonson (5), Pinner (6), Pappenheim (7), and Danchakoff (8) believe in the lymphocytic nature of these cells, while the Maurer-StShr (9, 10) school claims that these cells are epithelial in origin, though they appear like mesodermal lymphocytic cells. In addition they believe that these cells are capable of reverting to their original epithelial state.Since up to the present time no definite solution of the problem has been established, we believed that the method of autoplastic thymus transplantation with a detailed study of the histological changes which occur in the transplants from a few hours after their insertion to their 4O3 on

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